1. Technical Field of the Invention
The present invention relates to broadcast control channel (BCCH) carrier frequencies, and more particularly, to a method for changing a BCCH carrier frequency within a cell without disturbing ongoing call traffic within the cell or within neighboring cells.
2. Description of Related Art
Within cellular mobile telephone systems, there is a need from time-to-time to reconfigure the frequency plan of the system. The need for change arises from the growth of traffic within a cellular mobile telephone system that requires additional cells and/or tighter frequency reuse patterns. This causes frequency replanning to be one of the most time consuming tasks associated with the operation of mobile telephone networks. Presently, alterations to frequency reuse plans are normally performed during low traffic periods, such as at night. This is due to the fact that when the broadcast control channel (BCCH) carrier frequency is changed, the mobile stations served by the cell associated with the BCCH carrier frequency are unable to setup calls or camp on the specific cells.
While methods have been developed to change other carrier frequencies in a cell on a time-slot by time-slot basis, a similar technique has not presently been developed for changing the carrier frequencies associated with the BCCH channels. In fact, existing techniques require that time-slots altered, not be carrying the BCCH channel. The other solution involves completely disabling the BCCH carrier frequency in order to assign a new frequency. This change, as mentioned previously, is normally accomplished at night during low traffic periods. However, during this time period, nothing may be transmitted. This prevents call setup and causes all mobile stations within neighboring cells to be unable to provide signal strength measurements on the cell that is temporarily off-line. This prevents handoffs to the cell and may cause a handoff to a less suitable neighboring cell. The network could not rank an offline cell, which could potentially lead to a wrong handover decision or dropped call. Thus, there exist a need for a method enabling the changing of a BCCH carrier frequency without disturbing the call traffic presently existing on and associate with the cell in which the BCCH carrier frequency is being changed.